Roger Garrett, left, sits in court Monday in El Paso, Texas. Garrett is on trial in the slaying of his stepfather, former Green Beret Maj. Chester Garrett, in 1977. (Ruben R, Ramirez / The El Paso Times via AP)

EL PASO, TEXAS — A West Texas jury convicted a man Monday of helping his mother kill his stepfather in 1977, a case resurrected after the defendant’s brother told authorities he had confessed to the crime.

Roger Garrett was found guilty of murder after about eight hours of jury deliberations. He now faces five to 99 years in prison.

Garrett was accused of killing Army Maj. Chester Garrett and leaving his body in his car in the desert east of El Paso.

Patrick Garrett, who was 12 years old at the time of the death, told investigators that Roger Garrett had said that he had hit his stepfather in the head with a bat and their mother had stabbed him.

Roger Garrett’s ex-wife and a former girlfriend gave authorities similar accounts of Roger Garrett’s alleged admissions, the El Paso Times reported.

“Their stories are believable,” said Assistant District Attorney Denise Butterworth. “They are reasonable because their stories are the truth.”

Roger Garrett’s attorney, Ruben Morales, told jurors that his client never would have killed the man he considered his father.

Butterworth told jurors that witnesses said Roger Garrett was “tricked” into participating because his mother told him Chester Garrett abused her.

Prosecutors said Roger Garrett and his mother ambushed Chester Garrett at their home. Chester Garrett and his wife were separated at the time and had filed for divorce.

Butterworth said Lisbeth Garrett had motive because she found out her husband had a girlfriend and was preparing to move to Italy with her.

“Lisbeth can be divorced from a military officer, or the widow of a military officer,” Butterworth said. “They lied about this secret for 36 years. We are here because human emotion won out and solved this investigation. We are here because Roger couldn’t hold this in.”